Hydraulic control circuit

ABSTRACT

A plurality of valve units, each including a plurality of main valves connected in series in an idling conduit connecting the outlet of a control pump with a discharge space, is used for supplying hydraulic consumer motors with pressure fluid. Each main valve has an idling position for connecting the outlet of the pump with the discharge space through the idling conduit, and two operative positions for supplying and discharging fluid from the respective consumer motor, and for closing the idling circuit. Each main valve includes hydraulic operating means for shifting the main valve between idling and operative positions. A plurality of control valves supplies fluids to and discharge fluids from the hydraulic operating means, and a pressure control unit connects the idling conduit with the control valves. the pressure control unit includes a pressure reducing valve, a pressure fluid accumulator, a check valve between the accumulator and the pressure reducing valve so that a selected pressure is maintained in the hydraulic operating means when the respective main valve is in one of the operating positions. Preferably, a pressure limiting valve is arranged downstream of the pressure reducing valve, and has a higher pressure than the same. A pressurizing valve is provided between the idling conduit and the discharge space for maintaining a pressure in the idling conduit by which the operation of the operating means is started.

United States Patent [191 Zunzer HYDRAULIC CONTROL CIRCUIT [75]Inventor: Egon Zunzer, Lohr, Main, Germany [73] Assignee: G. L. RexrothGmbH, Lohr/Main,

Germany [22] Filed: Sept. 27, 1972 [21] Appl. No.: 292,696

[30] Foreign Application Priority Data Primary Examiner-Edgar W.Geoghegan Attorney, Agent, or Firm-Michael S. Striker [57] ABSTRACT Aplurality of valve units, each including a plurality of [4 June 18, 1974main valves connected in series in an idling conduit connecting theoutlet of a control pump with a discharge space, is used for supplyinghydraulic consumer motors with pressure fluid. Each main valve has anidling position for connecting the outlet of the pump with the dischargespace through the idling conduit, and two operative positions forsupplying and discharging fluid from the respective consumer motor, andfor closing the idling circuit. Each main valve includes hydraulicoperating means for shifting the main valve between idling and operativepositions. A plurality of control valves supplies fluids to anddischarge fluids from the hydraulic operating means, and a pressurecontrol unit connects the idling conduit with the control valves. thepressure control unit includes a pressure reducing valve, a pressurefluid accumulator, a check valve between the accumulator and thepressure reducing valve so that a selected pressure is maintained in thehydraulic operating means when the respective main valve is in one ofthe operating positions. Preferably, a pressure limiting valve isarranged downstream of the pressure reducing valve, and has a higherpressure than the same. A pressurizing valve is provided between theidling conduit and the discharge space for maintaining a pressure in theidling conduit by which the operation of the operating means is started.

8 Claims, 3 Drawing Figures Bier/L153 PATENTEDJIII 1 8 m4 SHEET 2 BF 2 Ei-a Fig.3

1 HYDRAULIC CONTROL CIRCUIT BACKGROUND OF THE INVENTION The presentinvention relates a hydraulic control circuit for hydraulic operation ofthe type in which the pressure fluid flows back to a low pressurecontainer in the position of rest of control valves. Hydraulic controlcircuits of this type are advantageously used for movable hydraulicapparatus, such as dredging apparatus.

In the prior art apparatus, the pressure fluid for the control valveswhich control the main valves, is supplied by a gear pump which isindependent of a main pump. It is also known to operate the controlvalves directly by pressure fluid taken from the main pump, eliminatinga separate control pump. The control pressure fluid is taken from themain operating fluid between the pump for the operating fluid and acontrol valve by means of an adjustable throttle together with apressure limiting valve which is adjusted to a position corresponding tothe maximum control pressure. If there is no control fluid required, thecontrol fluid is returned through the pressure limiting valve to the lowpressure discharge container. When the control fluid is taken betweenthe control valve and the low pressure container, a pressure controlledcheck valve with a throttle is disposed in the conduit leading to thedischarge container. The flow of working fluid is throttled by thethrottle to such an extent that the pressure required for the operationof the main valve, is obtained. The prior art apparatus of the type inwhich the control fluid for operating the main valves is influenced bythe main flow of working fluid, detrimentally affects the totalefficiency of the hydraulic apparatus, since part of the controlpressure fluid flows back to the low pressure container without beingused, while in another case the pressure level downstream of the mainvalve must be maintained at a high level. In addition to this loss ofefficiency, the developed heat loss must be compensated by the controlpressure fluid.

SUMMARY OF THE INVENTION It is an object of the invention to takecontrol pressure fluid for control valves from the flow of working fluidthrough the main valve, without causing substantial loss.

This object of the invention is obtained by a circuit in which theinitial control pressure for operating the main valves, andthe pressureof the working fluidflowing back to the low pressure discharge containerin the initial position of the main valves, correspond to each other.Furthermore, inaccordance with the invention, the control valves bywhich the positions of the main valves are controlled, include apressure reducing valve and a pressure fluid accumulator, a check valvebeing provided between the pressure fluid accumulator and the pressurereducingvalve. Due to the fact that the pressure of the circulatingfluid, and the initial control pressure for operating the main valvescorrespond to each other, it is assured that the main valves can beoperated starting with the initial position. The higher control pressurerequired after starting of the shifting of the main valves, is obtainedby throttling the circulating working fluid which causes a higherpressure in the sure is sufficient to move the main valves to thedesired position. The pressure-reducing valve limits the pressure of thecontrol fluid, and the additionally provided pressure fluid accumulatorassures an operation of the main valves, for example for lowering a loadto the ground, even if the pump fails.

In a preferred embodiment of the invention, where the hydraulic circuitincludes two or more pumps, the pressure fluid is taken from the mainflow through each of the pumps, and supplied to the pressure reducingvalve by a double check valve having two inlets and an outlet connectedwith the pressure reducing valve. This has the advantage that thecontrol fluid is branched off the flow of the pump which has the highestpressure. It is advantageous to combine the pressure reducing valve, thecheck valve, and the pressure limiting valve, together with theaccumulator, in a pressure control unit which is substantially a valveblock formed with bores in which movable valve elements are mounted.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagramatic viewschematically illustrating a hydraulic control circuit in accordancewith an embodiment of the invention, serving for operating a dredgingapparatus;

FIG. 2 is a sectional view taken on line Il--II in FIG. 3, andillustrating a pressure control unit in accordance with the invention;and

FIG. 3 is a sectional view taken on line III-Ill in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT A pump unit 1 includes twohydraulic pumps 3 and 4 whose displaced volume can be adjusted byoperation of a setting cylinder and piston means 5. An electric motor 6drives the two pumps 3 and 4. Pumps 3 and 4 pump pressure fluid throughconduits 7 and 12 to the inlets P1 and P2, respectively, of two valveunits 11 and 16. The pressure conduit 7 flows through an idling conduit23, 24, 25, 26 through three main valves 8, 9 and 10, when the mainvalves 8, 9 and 10 are in the illustrated idling position. From thepoint T the fluid flows through conduit 27 and discharge conduit 27a,and through pressurizing valves 55 and a check valve 55a into the lowpressure discharge container T from which pumps 3 and 4 suck fluid.Conduit 12 is connected at the point P of valve unit 16, with pressurefluid flowing through the idling conduit 28, 29,. 30, 31 and through themain valves 13, 14, 15 in the illustrated idling position to the point Twhich is connected by conduit 32 and discharge conduit 27a with theabove-described pressurizing valve means 55 and 55a.

Each of the main valves 8 to 10 and 13 to 15 has, in addition to theillustrated idling position, two operative positions for supplying anddischarging pressure fluid to associated hydraulic consumer apparatus 17to 19 and 20 to 22, the flow being reversed in the two operativepositions of the respective main valve.

For example, the working conduits A8 and B8 are connected with thevehicle drive means 17 on the left side of the vehicle, and the conduitsA13 and B13 are connected with the vehicle drive means 20 on the rightside of the vehicle. The working conduits A9 and B9 of the main valve 9are connected with an hydraulic cylinder and piston motor 18 whichoperates the arm of the dredging apparatus, and the working conduits A10and B10 of the main valve are connected with a hydraulic cylinder andpiston motor 19 which operates the scoop of the dredging apparatus.

The working conduits A14 and B14 of main valve 14 are connected with arotary hydraulic motor 21, and the working conduits A15 and B15 of mainvalve 15 are connected with the hydraulic cylinder and piston motor 22by which the boom is operated.

In the illustrated idling positions of main valves 8 to 10 and 13 to 15,the working conduits are closed except that in main valve 14, theworking conduits A14 and B15 are connected in valve 14 by a throttle14c.

The conduit sections 23, 24, 25 and 26 are connected with each other bythe main valves in the idling position, so that the fluid from pumps 3and 4 can flow through idling conduits 7, 23, 24, 25, 26, 27 and 12, 28,29, 30, 31, and 32 between the pump and the low pressure dischargeconduit 27a and discharge container T. The pressurizing valves 55maintain certain pressure in the idling conduits, and the check valve55a prevents return flow from the tank.

A pressure conduit 70 branches off the pump conduit 7, and a pressureconduit 120 branches off the pump conduit 12. Conduits 7a and 12a areconnected to inlets of a pressure control unit 2, which is shownschematically in FIG. 1 and in detail in FIGS. 2 and 3. As best seen inFIG. 3, the two inlets 7a and 12a cause the ball of the double checkvalve 33 to assume such a position that flow into the pressure controlunit 2 is possible only from the one of the conduits 7a and 12a in whichthe greater pressure prevails. The outlet 33a of the double check valve33 is connected with a pressure reducing valve 34, and the fluid atreduced pressure flows through a conduit 35 and the check valve 36 tothree control valve units 37, 38, and 39, each of which contains fourcontrol valves 40 to 43, 44 to 47, and 48 to 51. Control valves 40 and43 are connected by control conduits 40a and 43a to pressure chambers 9aand 9b of the main valve 9 so that the valve slide piston, not shown, ofmain valve 9 is shifted, as desired, between the illustrated idiingposition, and two operative positions in which the respective hydrauilcconsumer motor 18 is operated in forward or rearward direction,respectively. The control valves 41 and 42 of the control valve unit 37are connected by control conduits 41a, 42a to the control chambers 10a,10b of the main valve 10 cooperating with the hydraulic consumer motor19. The control valves 44 and 45 of the control valve unit 38 areconnected by control conduits 44a, 450 with the control chambers 8a, 8bof the hydraulic consumer motor 17 which drives the left drive means ofthe vehicle, while the control valves 46 and 47 of the same controlvalve unit 38 are connected by control conduits 46a, 47a with thecontrol chambers 13a, 13b of the main valve 13 which is associated withthe hydraulic motor 20 by which the drive means on the right side of thevehicle are operated.

The control valves 48, 51 of the control valve unit 39 are connected bycontrol conduits 48a, 51a with the control chambers 15a, 15b of thehydraulic motor 22 for operating the boom of the dredging apparatusunder the control of main valve 15, and the control valves 49 and 50 areconnected by control conduits 49a, 50a with the control chambers 14a,14b of the main valve 14 operating the rotary hydraulic apparatus 21 bywhich a support of a dredging apparatus is rotated.

In the illustrated idling position of the main valves 8 to 10, and 13 to15, pressure develops in the idling conduits 7, 23 to 26, 27 and 12, 28to 31, and 32 due to flow losses occurring in the ducts of the mainvalves and in the pressure conduits 7 and 12. If the flow losses are notsufficient to maintain a certain pressure in the idling conduits, thepressurizing valves 55 are provided to maintain the pressure in theidling conduits at a predetermined pressure which is still partlyproduced by the flow losses in the valve units 11 and 16.

The predetermined pressure produced and maintained in this manner in theidling conduit, corresponds to the control pressure required in theinitial operation of the main valves out of the illustrated circulationposition toward one of the two operative positions. A throttling of theflow cross section takes place which causes a further pressure increasein the respective pressure conduit 7 or 12 of the pumps 3 or 4. Thispressure increase is sufiicient for operating a respective main valvetoward one or the other selected operative end position. In theoperative end positions of the main valves 8 to 10, and 13 to 14, thehydraulic motors 17, 20, 21 and 18, 19, 22 are operated by pressurefluid, resulting in an average pressure corresponding to the power loadof the hydraulic consumer motors 17 to 19 and 20 to 22. The pressurereducing valve 34 in the pressure control unit 2 maintains the fluidpressure independently of the magnitude of the pressure of the fluid inthe working conduits and in the consumer apparatus. When control fluidunder pressure flows through the outlet conduit 35 of the pressurecontrol unit 2, the fluid pressure accumulator 52 is charged. In theevent that one of the pumps 3 or 4 fails, the check valve 36 prevents adischarge of the fluid from pressure fluid accumulator 52 into thepressure conduits 7 and 12, so that an amount of pressure fluid ismaintained in the accumulator for an emergency operation of the mainvalves 8 to 10 and 13 to 15.

A pressure limiting valve 53 which is arranged downstream of thepressure reducing valve 34, is set to a slightly higher pressure thanthe pressure reducing valve 34. Due to this arrangement, the supply ofcontrol fluid to the control valves 40 to 51 is assured, while at thesame time during normal operations, a discharge of fluid is effectivelyprevented.

FIGS. 2 and 3 illustrate the pressure control unit 2 in detail, and itwill be seen that a block 54 is provided with threaded bores 54a, 54b inwhich threaded plugs 12a and 12b are mounted which form the inletconduits 7a and 12a of the double check valve 33 whose outlet isconnected with the pressure reducing valve 34, which includes a spring34a, as best seen in FIG. 2. Downstream of the pressure reducing valve34, the pressure limiting valve 53 includes a spring 53a acting on apointed valve member cooperating with a valve seat 53b. A dischargeconduit 530 communicates with a low pressure discharge container T.

The pressure control unit illustrated in FIG. 2 and 3 requires onlyconnectors for the branch conduits 12a and 7a, and for the conduit 35which is connected with the control valves 40 to 51. The pressure fluidaccumu lator 52 has a threaded portion secured in a threaded bore 52a ofthe block 54.

The accumulator is connected with the conduit 35 via the valve body 36which is provided with a (not visible) blind bore. The lattercommunicates via bores 36a and via bores 360 of the member 36b with aspace 35d, which in turn communicates with outlet 35c (FIG. 3) leadingto conduit 35.

The threaded connectors permit a very quick connection of the pressurecontrol unit 2 with the respective conduits.

Only two valve units 11 and 16 have been shown, but it is understoodthat a greater number could be provided. If more than two pumps 3 and 4are provided, the check valve means 33 have to be accordinglyconstructed to permit flow into the pressure control unit 2 only fromthe pump operating at the highest pressure.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofhydraulic control circuits differing from the types described above.

While the invention has been illustrated and described as embodied in ahydraulic control circuit, particularly for dredging apparatus, providedwith a pressure control unit for reducing the pressure provided by apump to the pressure suitable for hydraulic operation of main valves 8to 10 and 13 to 15, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

1 claim:

1. Hydraulic control circuit, comprising a control pump having an outletfor pressure fluid; a discharge space; idling conduit means between saidoutlet of said pump and said discharge space; at least one valve unitincluding a plurality of main valve means connected in series in saididling conduit, and being respectively associated with hydraulicconsumer motors, each main valve means having an idling position forconnecting said outlet of said pump with said discharge space throughsaid idling conduit, and at least one operative position for supplyingfluid to, and discharging fluid from the respective consumer motor, andfor closing said idling conduit, each main valve means includinghydraulic operating means for shifting said main valve means betweensaid idling and operative positions; a plurality of control valve meansfor supplying fluid to, and for discharging fluid from said hydraulicoperating means, respectively; and a pressure control unit connectingsaid outlet of said pump and idling circuit with said control valvemeans so that in said idling position the initial pressure in saididling conduit starts said operating means, said pressure control unitincluding pressure reducing valve means, a pressure fluid accumulator,and a check valve between said accumulator and said pressure reducingvalve means opening toward the former so that a selected pressure ismaintained in said hydraulic operating means when said main valve meansis in said operative position.

2. Hydraulic control circuit as claimed in claim 1 comprisingpressurizing valve means between said idling conduit and said dischargespace for maintaining a pressure in said idling conduit in said idlingposition of said control valve means. i

3. Hydraulic control circuit as claimed in claim 2 wherein saidpressurizing valve means includes a check valve opening towards saiddischarge space.

4. Hydraulic control circuit as claimed in claim 1 wherein said pressurecontrol unit includes a pressure limiting valve downstream of saidpressure reducing valve, said pressure limiting valve being set to ahigher pressure than said pressure reducing valve.

5. Hydraulic control circuit as claimed in claim 1 comprising twocontrol pumps; two idling conduits; two valve units; and wherein saidpressure control unit includes a shiftable double check valve having twoinlets connected near outlets of said pumps with said idling conduits,respectively, and one outlet connected with said pressure reducing valvemeans.

6. Hydraulic control circuit as claimed in claim 5 wherein said pressurecontrol unit includes a pressure limiting valve downstream of saidpressure reducing valve, said pressure limiting valve being set to ahigher pressure than said pressure reducing valve means; and whereinsaid pressure control unit includes a valve block formed with bores inwhich said pressure reducing valve means, said pressure limiting valvemeans, and said double check valve are located, and having a threadedbore into which said accumulator is threaded.

8. Hydraulic control circuit as claimed in claim 1 wherein each mainvalve means has two operative positions and said idling position; andwherein said consumer motors are reversed in said two operativepositions.

1. Hydraulic control circuit, comprising a control pump having an outletfor pressure fluid; a discharge space; idling conduit means between saidoutlet of said pump and said discharge space; at least one valve unitincluding a plurality of main valve means connected in series in saididling conduit, and being respectively associated with hydraulicconsumer motors, each main valve means having an idling position forconnecting said outlet of said pump with said discharge space throughsaid idling conduit, and at least one operative position for supplyingfluid to, and discharging fluid from the respective consumer motor, andfor closing said idling conduit, each main valve means includinghydraulic operating means for shifting said main valve means betweensaid idling and operative positions; a plurality of control valve meansfor supplying fluid to, and for discharging fluid from said hydraulicoperating means, respectively; and a pressure control unit connectingsaid outlet of said pump and idling circuit with said control valvemeans so that in said idling position the initial pressure in saididling conduit starts said operating means, said pressure control unitincluding pressure reducing valve means, a pressure fluid accumulator,and a check valve between said accumulator and said pressure reducingvalve means opening toward the former so that a selected pressure ismaintained in said hydraulic operating means when said main valve meansis in said operative position.
 2. Hydraulic control circuit as claimedin claim 1 comprising pressurizing valve means between said idlingconduit and said discharge space for maintaining a pressure in saididling conduit in said idling position of said control valve means. 3.Hydraulic control circuit as claimed in claim 2 wherein saidpressurizing valve means includes a check valve opening towards saiddischarge space.
 4. Hydraulic control circuit as claimed in claim 1wherein said pressure control unit incLudes a pressure limiting valvedownstream of said pressure reducing valve, said pressure limiting valvebeing set to a higher pressure than said pressure reducing valve. 5.Hydraulic control circuit as claimed in claim 1 comprising two controlpumps; two idling conduits; two valve units; and wherein said pressurecontrol unit includes a shiftable double check valve having two inletsconnected near outlets of said pumps with said idling conduits,respectively, and one outlet connected with said pressure reducing valvemeans.
 6. Hydraulic control circuit as claimed in claim 5 wherein saidpressure control unit includes a pressure limiting valve downstream ofsaid pressure reducing valve, said pressure limiting valve being set toa higher pressure than said pressure reducing valve means; and whereinsaid pressure control unit includes a valve block formed with bores inwhich said pressure reducing valve means, said pressure limiting valvemeans, and said double check valve are located, and having a threadedbore into which said accumulator is threaded.
 7. Hydraulic controlcircuit as claimed in claim 5 wherein said two control pumps includeadjusting means for adjusting said control pumps to discharge fluid atdifferent pressures at said outlets, respectively.
 8. Hydraulic controlcircuit as claimed in claim 1 wherein each main valve means has twooperative positions and said idling position; and wherein said consumermotors are reversed in said two operative positions.